Grease compositions



deterioration of the greases.

tion of grease deterioration involves inhibiting i atenteci Oct. 21, 1952 Califl, assig'riors to California Research Corpus ration, San' Francisco, Calif., a corporation of Delaware No Drawing. Application il) ec ember 7, 1950, Serial No. 199,725

8 Claims. 1

The invention pertains to the improvement in oxidation resistance of grease compositions and the like. Particularly, this invention pertains to the use of a polyvalent metal salt of a dithiocarbamic acid (e. g., zinc dibutyl dithio-caibamate) in combination with a hydroxy anthraquinone (e. g., alizarin) in grease compositions to increase the oxidation stability of the grease.

The selection of greases for particular jobs involves more than the selectiono'i a grease because of its general appearance at room temperature, its consistency at room temperature, its extreme pressure characteristics; it's melting point, etc. The selection of greases must be accompanied by assurance that the grease will maintain its grease characteristics and perform its duties over wide ranges of temperature and wide variances in pressures at the surfaces being lubricated forlong periods of time.

It is essential that the grease composition be resistant to oxidation while it is performing the specific task of lubricating such parts as found in automotive wheel bearings, sealedbearings of electric motors, sealed bearings of compressors, steel mill equipment, high speed motors, universal joints, rocker arms of airplane motors, armature bearings of diesel engines, etc.

It has been found that the problem concerned with the inhibition of oxidation of fluid lubricating oil compositions is normally difierent from the problem dealn with oxidationinhibition of greases. Lubricating oil oxidation-inhibitors do not always exert the same effect of preventing serious oxidative deterioration when incorporated in greases. The acid salts or soaps' used as thickening agents in greases appear to be major'factors'in contributing to the oxidative Thus, the preventhe destructive oxidation of the metallic'thickening agent itself, or the oxidation of the oil component as catalyzed by the presence of the'metal compound, "or inhibitin'g'bdth types of oxidation simultaneously.

When greases are prepared, there is a certain grease structure, that is, a gel type structure which is the fundamental characteristic of each type of a grease; However, this structure is not maintained overwide ranges of temperatures and pressures for long'periods of time if the grease is not resistant to oxidation. Although numeroils agents are available for inhibiting oxidation of greases for a varied length of time, the agents normally do not inhibit oxidation of the grease compositions long enough to use the inhibited 'greasecoinp'osition in sealed bearings, for ex- I ample, and the like.

A detrimental result of the oxidationof grease compositions during the period of lubr the loss in thickening power. of theth clening agent (e. 'g., the soap) used in the grease composition. When greases lubricate the desired surfaces, the greases normally become quite warm. When h'ot greases become oxidized, they lose their grease structure in the form or melt, This men then nowsawa from the surfaces being lubricated, thereby producing lubrication failure. In some greases, the melt, upon c mmenta etion, becomes hard and brittle, thereby'affording no lubrication'of the surfaces. In some instances, the nielt be omes oxidized to the de ieewhere acids are formed, which acids may corrode the surfaces which are to be lubricated.

It is a tremendous advantage i lubrication systems which are not readily acd ble to use grease compositions which withstand hightemperaturesandthe effects of oxidation for long periods of time; that is, it is highly desirable to use grease compositions such instances which do not require changes for long periods of time.

Although the problems pertaining to oxidation of greases are more prevalentathigh temperatures, these same problems may be ncc'uiitered in a minor degree when the greases are suH-Jected to lower temperatures during the lubrication 'of bearings, etc.

Greases which are not highly o'xidaticn' resistant cannot be used at the maximum usable temperature desired when lubricating bearings, wheel assemblies, etc. Grease compositions have certain fundamental desirable properties, and it is an object to retain those properties in the grease throughout wide ranges of temperatures, pressures, and periods of time. With the incorporation of the combinations of compounds described herein, the useful life of a grease at high temperatures is markedly extended.

It is an object of this invention to set forth grease compositions which are highly resistant to oxidation.

It is a, further object of this invention to' prepare grease compositions which maintain their grease structure throughout wide changes in temperature.

It is another object of this invention to enhance still further the oxidation resistance of greases containing oxidation inhibitors by incorporating therein an agent which is relatively ineffective as a grease oxidation inhibitor,

These and further objects of this invention will 3 be apparent from the following description and the appended claims.

In accordance with this invention, it has been found that grease compositions which retain their grease-like characteristics throughout wide ranges of temperatures and pressures over long periods of time can be prepared by incorporating polyvalent metal dithiocarbamates and hydroxy anthraquinones in combination in grease compositions. effect enhances the stability of a grease composition, particularly the oxidation resistance of a grease composition, so that the greases are highly satisfactory for lubricating inaccessible points, sealed bearings, and the like. The desirable characteristics of a grease composition containing a polyvalent metal dithiocarbamate are markedly enhanced when a hydroxy anthraquinone is added thereto.

The grease composition of the present inven- 'tion consists essentially of a lubricating oil, a

thickening agent, a polyvalent metal salt of a dithiocarbamic acid and a hydroxy anthraquinone.

Suitable lubricating oils include a wide variety I of oils, such as naphthenic base, paraffin base and mixed base mineral oils, synthetic oils, e. g., alkylene. oxide polymers such as polypropylene oxide polymers, and other hydrocarbon lubricants, e. g., lubricating oils derived from coal products. Other synthetic oils include esters of alkylene oxide-type polymers, e. g., acetylated propene oxide polymers prepared by acetylating propene oxide polymers containing hydroxyl groups, dicarboxylic acid esters, polyesters, esters of polyhydric alcohols and liquid esters of acids of phosphorus and silicon.

The thickening agents which are suitable for v the purposes of grease formation are any thickening agents satisfactory in themselves to form a grease. Most commonly employed for this purpose are organic acid metal salts, which may be represented by the formula wherein R. represents a saturated or unsaturated alkyl group or an aralkyl group, the R group having from 10 to about 30 carbon atoms, 16 to 22 carbon atoms being preferred; X represents a carboxy group if (i. e., aC-O group) a phosphonyl group (i. e., a1 O group) ()3 a sulfonyl group 0 (i. e., a-SO- group) 9) or a sulfate group 0 (i. e., a0 HO group) and M represents a metal of groups 1 and 2 of the periodic table, specifically, calcium, barium strontium, aluminum, and combinations thereof; n represents an integer having a value of 1, 2, or 3, depending on whether M is monovalent or divalent or trivalent.

A synergistic effect is obtained; which The hydrogen of the R group may be sub 'stituted by polar groups such as chlorine, bromine, ether, hydroxy, mercapto, etc.

Examples of the organic acids which may be used in the formation of the metal salts include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, arachidic acid, melissic acid, phenyl acetic acid, cetyl benzoic acid, acids resulting from the oxidation of petroleum products (e. g., Waxes), cetane sulfonic acid, dodecyl benezene sulfonic acid, dodecane phosphonic acid and lauryl sulfuric acid.

Other thickening agents include alkyl ammonium bentonites (i. e., bentonite treated with quaternary ammonium compounds), graphite, fumed silica, etc.

The polyvalent metal dithiocarbamates are oil-soluble compounds of the generic formula:

wherein the Rs represent straight-chained or branch-chained, saturated or unsaturated essentially hydrocarbon (hydrocarbonaceous) radicals; the Rs containing sufiiciently large hydrocarbon groups to render the dithiocarbamates oil-soluble. It is preferred that each R group contain from 4 to 20 carbon atoms. The R groups may or may not be identical. M represents a polyvalent metal, and n represents the'valence of the polyvalent metal. 7

Examples of the R groups include ethyl, propyl, propenyl, butyl, butenyl, octyl, octenyl, octadecyl,

v benzyl, phenyl butyl, phenyl octyl, ethyl phenyl,

butyl phenyl, octyl phenyl, etc.

By essentially hydrocarbon (hydrocarbonaceous) radical is meant those radicals which are composed mainly of hydrogen and carbon, and includes such radicals which contain, in addition, minor amounts of substituents such as chlorine, bromine, oxygen, hydroxyl groups, etc.

Dithiocarbamates in which the nitrogen is a part of a ring may also be used,.as in the dithiocarbamates produced by reacting piperidine, alkyl piperidines and reduced petroleum nitrogen bases with carbon disulfide in the presence of caustic alkali.

The thiocarbamates of this invention are exemplified by the following: polyvalent metal dibutyl dithiocarbamates, diamyl dithiocarbamates, dicetyl dithiocarbamates, methyl octyl dithiocarbamates, butyl amyl phenyl dithiocarbamates, petroleum base dithiocarbamates. di-(amyl piperidyl) dithiocarbamates, zinc dibutyl dithiocarbamate, cadmium dibutyl dithiocarbamate, zinc diamyl dithiocarbamate, zinc dicetyl dithiocarbamate, zinc methyl octyl dithiocarbamate, zinc .petroleum base dithiocarbamate, etc.

General methods of preparing thiocarbamates are available in the literature. For example, a primary or secondary amine is heated with carbon disulfide and aqueous or alcoholic caustic potash to produce the alkali metal dithiocarbamate. Polyvalent metal salts of dithiocarbamic acids are formed by double decomposition of the alkali metal salts of the dithiocarbamic acids and water-soluble polyvalent metal salts. An aqueous solution of a polyvalent metal salt (e. g., zinc sulfate) is added to the alkali metal dithiocarbamate solution, thereby precipitating the desired polyvalent metal 7dithiocarbamate. The polyvalentmetals include zinc, cadmium, calcium, lead, aluminum, iron and-barium. It ispreferred t use zinc and cadmium dithiocarbamates.

The preparation"-of petroleuin base 'dithiocarbamates is described-in detail in Miller and Rutherford Patent No. 2,363,012, filed May 6,

1%942, and which issued on November 21, 1944.-

The hydroxy anthraquinonesof this invention include anthraquinones containing at least one- 'hydroxyl group on the ring-such as exemplified by l-hydroxy anthraquinone, alizarin (1,2-dihydroxy ahthraquinone), quinizarin'" (L l-dihydroxyanthraquinone); anthrarufin (1,5-

I dihydroxy anthraquinone') and ch-rysazin (1,8-

"ates of this invention.

-The thickeningagents are incorporated in the "-compositi'on ofthis invention-in amounts sufficient to form the grease. J Such amounts as about 3% to about 50% (based on the finished'composition) can be used.-- However, about "7% to about 25% are the preferred amounts.

The dithiocarbamates of this invention are used in amounts sufiicient to increase the oxidation stability of grease compositions, particularly, from about 0.1% to about 0.5% to about 2.0% being especially preferred.

The amounts of hydroxy anthraquinones which are used in conjunction with the dithiocarbamates of this invention are from about 0.0l to about 2% by weight based on the final composition. Certain of the hydroxyanthraquinones are more oil-soluble than others, and the amount of that hydroxy anthraquinone which can be used is thus dependent upon the solubility of the anthraquinone in the particular grease stock.

In order to make it more convenient for shipping purposes, etc., as much as 10% or more of the polyvalent metal dithiocarbamates and as much as 10% or more of the hydroxy anthraquinones may be'dispersed in a grease base stock composition.

The dithiocarbamates and the hydroxy anthraquinones can be incorporated in the grease compositions in various ways, as by addition to the mineral component of the grease before compounding the grease, by addition during the compounding of the grease or by addition to the finished grease. Generally, some degree of heating is advisable during incorporation of the dithiocarbamates and the hydroxy anthraquinones in the grease, to hasten their solution or dispersion.

It is not essential that the dithiocarbamates and the hydroxy anthraquinones be incorporated in the grease composition together. The hyd-roxy anthraquinones may be incorporated in grease compositions containing the dithiocarbamates.

As noted from the data hereinbelow, the polyvalent metal dithiocarbamates in themselves improve the desirable properties ofgreases, particularly the oxidation resistance of grease compositions, to a certain degree. On the other atures.

hand, hydro'x'y anth-raquinones in themselves are relatively ineffective in this respect. However, when hydroxy anthraquinones are added to grease compositions containing polyvalent metal dithiocarbamates, the grease compositions retain their grease-like characteristics for considerably longer periods of time than possible with polyvalent metal dithiocarbamates alone.

The greases of the present invention were subjected to a thin film test which measures the ability of the grease composition to maintain grease-like characteristics, particularly, retention of pliability and resistance to oxidation under exposure of a thin film to high temper- The test also indicates other grease characteristics, such as tendency to bleed, fiake (some greases, although'soft andfgreasy, crack and flake) andtendency to becometacky}, '{Ihe thin film test is as follows:

The grease to be tested is coated .on-a'metal strip. The grease coating is .of uniform dimensions: inch thick, '78 inch wide, and 2 /2 7 inches long. This grease sample is placed in an oven at 250 F. and observed at periodicintervals until the sampleno longer exists as a grease. The life of the. grease is the-number of hours during which the g-rea-se sample may beso heated before it loses itsgrease-like characteristics, that is, the time at which the test sample begins'ftobecome'hardand brittle. j v

The following Table 1 presents data obtained by the thin film test showing the effectiveness ,of hydroxy anthraquinones in extending the life of grease compositions containing polyvalent metal dithi-ocarbam-ates. The greases used in these tests were prepared as follows:

A mixture of 13.8 parts by Weight of lithium stearate, 1.7 parts by weight of calcium stearate, 33.8 parts by weight of a California solvent-refined paraffinic base oil having a viscosity of 356 SSU at 100 F., and 50.7 parts by weight of a California solvent-refined parafiinic base oil having a viscosity of 98 SSU at 100 F. was heated up to 420 F. and that temperature maintained for 15 minutes. The mixture was cooled to room temperature and milled. The desired amounts of polyvalent metal dithiocarbamates and hydroxy anthraquinones were then blended into the grease.

Table I Amount of Hydroxy Z '1 1 1% D i l 1 1t 3 l PAuthmquimPe Life of Dithiocarcent by Welght) Grease bamate (Percent (Hours) by M t) Alizarin Quinizarin '7 Table II presents data for the thin film tests run with the same base grease as in Table I, using a cadmium dithiocarbamate.

In additionto the components noted hereinabove, the grease composition may include such other additives as various corrosion inhibitors, extreme pressure agents, antiwear agents, stabilizers, V. I. improvers, and the like, provided that they do not interfere with the oxidation stability of the grease.

, We claim:

1. A grease composition consisting essentially of a major portion of a lubricating oil, a thickening agent, and from about 0.1% to about by weight, of a polyvalent metal dithiocarbamate, and from about 0.01% to about 2%, by weight, of a dihydroxyanthraquinone.

2. The grease composition of claim 1, wherein the polyvalent metal dithiocarbamate is a zinc dialkyl dithiocarbamate.

3. The grease composition of claim 1, wherein the polyvalent metal dithiocarbamate is a cadmium dialkyl dithiocarbamate.

4. The grease composition of claim 1 wherein the polyvalent metal dithiocarbamate is zinc dibutyl dithiocarbamate.

5. The grease composition of claim 1 wherein the dihydroxyanthraquinone is alizarin.

6. The grease composition of claim 1 wherein the dihydroxyanthraquinone is quinizarin.

'7. The grease composition of claim 1 wherein the thickening agent is a lithium soap.

8. The grease composition of claim 1 wherein the thickening agent consists of a lithium soap and a calcium soap.

" JOHN L. DREHER. I

CRAWFORD F. CARTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,016,648 OreIup Oct. 8, 1935 2,053,421 Burk et a1. Sept. 8, 1936 2,160,880 Loane et a1. June 6, 1939 2,214,443 Varteressian Sept. 10, 1940 2,338,578 Downing et a1. Jan. 4, 1944 2,400,106 Denison et al May 14, 1946 2,504,672 Farrington et a1. Apr. 18, 1950 

1. A GREASE COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PORTION OF A LUBRICATING OIL, A THICKENING AGENT, AND FROM ABOUT 0.1% TO ABOUT 5%, BY WEIGHT, OF A POLYVALENT METAL DITHIOCARBAMATE, AND FROM ABOUT 0.01% TO ABOUT 2% BY WEIGHT, OF A DIHYDROXYANTHRAQUINONE. 